Methods for reconstructing tomographic image datasets from detector data from a scan of an object by a CT system are generally known. If metal items are located in the object, strong image artifacts, known as metal artifacts, which appreciably reduce the quality of the reconstructed image, arise on account of increased beam hardening, more scattered radiation, a partial volume effect and increased noise.
To reduce such metal artifacts a wide variety of methods is known. These can be divided into three groups:                Interpolation-based methods, as described for example in the publications W. A. Kalender, R. Hebel, and J. Ebersberger, “Reduction of CT artifacts caused by metallic implants,” Radiology, vol. 164, no. 2, pp. 576-577, August 1987, and A. H. Mahnken, R. Raupach, J. E. Wildberger, B. Jung, N. Heussen, T. G. Flohr, R. W. Gunther, and S. Schaller, “A new algorithm for metal artifact reduction in computed tomography: in vitro and in vivo evaluation after total hip replacement,” Investigative Radiology, vol. 38, no. 12, pp. 769-775, December 2003. The group of interpolation methods also includes an improved method for normalized sinogram interpolation, which is disclosed in the applicant's patent application DE 10 2009 032 059 A1.        Empirical methods, in which individual physical effects are corrected, as described for example in the publications M. Kachelrieβ, O. Watzke, and W. A. Kalender, “Generalized multi-dimensional adaptive filtering (MAF) for conventional and spiral single-slice, multi-slice and cone-beam CT,” Med. Phys., vol. 28, no. 4, pp. 475-490, April 2001, and Y. Kyriakou, E. Meyer, D. Prell, and M. Kachelrieβ, “Empirical beam hardening correction (EBHC) for CT”, Med. Phys., 37(10):5179-5187, October 2010.        Iterative correction methods, which are described for example in the publications B. De Man, J. Nuyts, P. Dupont, G. Marchal, and P. Suetens, “An iterative maximum-likelihood polychromatic algorithm for CT,” IEEE Transactions on Medical Imaging, vol. 20, no. 10, pp. 999-1008, October 2001. and C. Lemmens, D. Faul, and J. Nuyts, “Suppression of Metal Artifacts in CT Using a Reconstruction Procedure That Combines MAP and Projection Completion”, TMI, vol. 28, no. 2, pp. 250-260, February 2009.        
Although the above-mentioned methods sometimes produce very good results, residual artifacts always remain, and need to be eliminated.